JPH0270379A - Method of welding pipe formed by composite heat source - Google Patents

Abstract

PURPOSE:To improve a welding speed by specifying the distance between a high-frequency induction heating source and squeeze rolls to a specific size or above and the inter-edge size of an open pipe to a specific size or below without providing an impeder in combination with the above-mentioned heating source. CONSTITUTION:The open pipe 1 with the edges 3 faced upward is passed through a high-frequency heating coil 3. The edges 2 and the periphery thereof are preheated at this time. The squeeze rolls bring the edges 2, 2 into contact with each other on the downstream thereof and laser light 4 melts the edges so that the open pipe 1 is made into a pipe 10. Electromagnetic force is increased too much and the instability of the molten metal is caused when the impeder is combined with the high-frequency induction heating source. The distance between the centers of the high-frequency induction heating source and the squeeze rolls is set at >=4 times the outside diameter of the pipe. The molten metal is unstable if the distance is below 4 times. The energy is saved if the distance between the edges 2 and 3 is confined to <=4mm. Since the molten meal is stabilized, the increase of the preheating temp. is possible and the welding speed is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a pipe manufacturing welding method using a composite heat source that combines an electric resistance welding method with a direct heating fusion welding method such as plasma welding or laser welding.

[Prior Art] As one of the pipe manufacturing methods, a method is known in which a skeleton is formed into a zero shape to produce an oven pipe or a welded pipe. The most reliable welding method used in this pipe manufacturing method is
The method is based on plasma welding or TIG welding. However, these methods have low welding speeds and low efficiency.

That is, when high-speed plasma welding is performed, a keyhole is not formed due to insufficient penetration, and a streamflow bead is generated, making it difficult to form a stable bead. Furthermore, in the case of TIG welding, discontinuous beats called humping occur during high-speed welding due to the arc force and the surface tension of the molten metal. Therefore, these methods are used only for manufacturing high-grade pipes such as stainless steel pipes and high-alloy steel pipes, where quality is more strongly required than efficiency.

On the other hand, the most efficient pipe manufacturing welding method is the electric resistance welding method (
(hereinafter referred to as ERW). However, the target is limited to general carbon steel pipes such as steel pipes for machine structures, and high-grade pipes are excluded. This is because ERW is inherently prone to minute welding defects, and special measures such as shield welding must be taken when applied to high-grade pipes, and even if such measures are taken, they may not be sufficient. The reason is that it is difficult to obtain results.

By the way, micro welding defects in ERW are caused by the electric force caused by high-frequency current. In other words, ERW applies high-frequency current in opposite directions to the edges to be joined, making use of the skin effect and proximity effect. This is a welding method that melts the edges, and as a result, a strong electromagnetic force acts on the molten metal at the abutting point of the image edge.As a result, the molten metal flows away from the abutting point. The position of the meeting point changes periodically due to the ejection and the accompanying shape changes and electrical load fluctuations.ER
It is thought that the micro welding defects that occur with W are caused by instability of pressurized solidification due to positional fluctuations of this abutting point.

On the other hand, these welding defects are mainly caused by oxides of Mn and Si, and are also caused by the fact that the ERW is melted and joined in the atmosphere. Therefore, by shielding the molten metal with an inert gas or the like, it is possible to significantly reduce defects even if the positional fluctuation of the abutment point is left undisturbed. but,
In stainless steel or high alloy steel that contains a large amount of alloying elements that are easily oxidized (for example, Cr), defects cannot be completely prevented even if this shield welding is performed. Micro defects that occur in ERW are difficult to detect through non-destructive testing, so
If defects cannot be completely prevented, sufficient reliability cannot be obtained, making it difficult to apply to high-grade pipes.

A pipe manufacturing welding method using a composite heat source was developed against this background, and is a method that combines reliability comparable to plasma welding and TlO2 welding and efficiency comparable to ERW. This method is a combination of ERW and direct heating fusion welding methods such as plasma welding and laser welding, as shown in Japanese Patent Application Laid-Open No. 168981/1981. This is a method of preheating with a heat source and then melting with a second heat source such as plasma heating or laser heating immediately before bonding and bonding under pressure. According to this method, the edges are finally melt-welded, so there are no weld defects that are a problem with ERW, and since preheating is performed, there are no weld defects that occur when high-speed welding is performed with plasma welding etc. High-speed welding is possible without the occurrence of streamer bead, humping bead, or lack of penetration.

[Problems to be Solved by the Invention] However, in the pipe manufacturing welding method using such a composite heat source, when the output of the high-frequency induction heating means, which is the first heating source, is increased in order to increase the preheating temperature, the collision point Molten metal is discharged to the inner and outer sides of the pipe, resulting in excessive build-up height and formation of discontinuous beads. Therefore, the preheating temperature is limited and the welding speed is also limited.

By the way, conventionally in ERW, an impeder has been placed on the inner surface side of the pipe in the area where the high-frequency induction heating means is installed for the purpose of improving electrical efficiency. Similarly, in the above-described pipe manufacturing and welding method using a composite heat source, an impeder is used as the first heat source. In order to prevent the increase in the height of the overlay and the formation of discontinuous beads due to the increase in the output of the first heating source,
It is considered effective to remove this impeder and also move the high frequency induction heating means away from the squeeze roll, but on the other hand, it becomes difficult to centrally heat the edges, and this greatly reduces electrical efficiency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pipe manufacturing and welding method using a composite heat source, which makes it possible to increase preheating temperature and increase welding speed without reducing electrical efficiency.

[Means for solving the problem] In a pipe manufacturing welding method using a composite heat source, an increase in the height of the reinforcement and the formation of discontinuous beads occur when the output of the high-frequency induction heating means, which is the first heating source, is increased. The main reason for this is thought to be an increase in high-frequency electromagnetic force at the collision point. In order to reduce the high-frequency electromagnetic force at the abutment point, it is necessary to prevent high-frequency current from flowing through the abutment point. To achieve this, it is effective to not use an impeder and to separate the heating means from the squeeze roll.

However, this reduces electrical efficiency and significantly increases the amount of high-frequency manual power needed to heat the edge to a constant temperature, leading to an increase in energy costs.

The present inventors have determined that it is effective to reduce the distance between the edges of the open pipe in order to prevent a decrease in electrical efficiency when the heating means is separated from the squeeze roll without using an impeder. .

In ERW, the distance between the edges is necessarily set large because the larger the angle formed by the image edges at the abutting point, the better the weldability. In other words, when the distance between the edges is small and the angle formed by both edges at the meeting point becomes small,
A short circuit occurs in the molten metal between the edges before joining, and the abutment point is not maintained stably, resulting in frequent welding defects. When the heating means is separated from the squeeze roll, the distance between the edges at the heating means installation position becomes even larger.

According to the findings of the present inventors, when the distance between the edges is made small, in normal ERW, the molten metal becomes unstable at the meeting point, resulting in frequent welding defects, but in ERW, the edges are not melted but only preheated. This problem does not occur if
It has become clear that only the deterioration in electrical efficiency caused by omitting the impeder and separating the heating means from the squeeze roll can be effectively improved by utilizing the proximity effect.

The present invention was made based on this knowledge, and after preheating the opposing edges of the open pipe to a temperature below the melting point of the material using a first heating source using high frequency induction, a second heating process is performed near the squeeze roll. In the pipe manufacturing welding method in which the edge portion is melted by a source and joined under pressure, the first
An impeder is not provided in the heating source, and the distance between the centers of the first heating source and the squeeze roll is at least four times the outer diameter of the pipe, while the distance between the edges at the position of the first heating source is The gist of the present invention is a pipe manufacturing welding method using a composite heat source characterized by a power of 41 W or less.

In the method of the invention, the preheating region of the edge portion by the first heating source is preferably gas-shielded.

[Function] The reasons for limiting the conditions in the method of the present invention are as follows.

In manufacturing welding methods using ERW and conventional composite heat sources, it is essential to improve electrical efficiency, but when the output of the high-frequency induction heating means, which is the first heating source, is increased, high-frequency electromagnetic force at the abutment point Excessive
An impeder should not be combined with the high-frequency induction heating means, as this would make the molten metal unstable.

Center open circuit M between the first heating source and the squeeze roll: If the output of the first heating source is increased when this distance is less than four times the outer diameter of the pipe, an The molten metal at the junction becomes unstable, resulting in an increase in the height of the build-up and the formation of discontinuous beats. Therefore, this distance should be at least four times the outer diameter of the pipe.

Distance between edges at the first heating source position: When the impeder is omitted and the distance between the centers of the first heating source and the squeeze roll is set to four times or more the outer diameter of the pipe, the reduction in electrical efficiency is suppressed and energy costs are reduced. The diameter should be 4 mm or less in order to reduce the By the way, if you set the distance between the high frequency heating means and the squeeze roll in ERW to be more than four times the outside diameter of the pipe,
The distance between the edges at the high frequency heating means is about 6 mm or more. Even in the conventional pipe manufacturing welding method using a composite heat source, the distance between the edges at the first heat source position is set to this extent.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

The open pipe 1 is continuously formed from a skeleton (not shown). That is, a skeleton (not shown) is first formed into a U-shaped cross section using a group of forming rolls, and further formed into an O-shaped cross section to form the open pipe 1.

The formed open pipe l has opposite edges 2.
It passes through the high-frequency heating coil 3, which is the first heating source, with the part 2 facing upward, and then passes through the squeeze roll on the downstream side.

When the oven pipe 1 passes through the high frequency heating coil 3, the edges 2, 2 and their surroundings are preheated.

The preheated edges 2, 2 contact the squeeze roll slightly before the center. The contact portion is melted from above by laser light 4 from a laser light generator, which is a second heating source. The molten parts are pressed and bonded while passing between squeeze rolls.

Thus, open pipe l becomes pipe 10.

At this time, no impeder is combined with the high-frequency heating coil 3, and the distance between the center c1 of the heating coil 3 and the center C2 of the squeeze roll is set to be at least four times the outer diameter of the pipe 1o. Furthermore, the distance G between the edges 2, 2 at the high frequency heating coil 3 is set to 4 or less.

Instead of the high frequency heating coil 3, a contact chip connected to a similar high frequency power source may be slidably contacted to the edge 2.2. Further, instead of laser light, another direct heating source such as plasma may be used as the second heating source.

Figures 2 (a) to (C) illustrate the effects of the center-to-center distance between the heating coil center and the squeeze roll center C2 and the edge-to-edge distance G at the heating coil position on the high current density region caused by the heating coil. be. The high current density region is a high temperature heating region (300'C or more) when static heating is performed at a speed of 20 m/min with an electric power that can ensure a preheating temperature of 1200'C or more, and is indicated by diagonal lines. Moreover, the outer diameter of the pipe after welding is 34 mm.

When the center-to-center distance is 80cm, which is about twice the pipe outer diameter, the edge opening NG is 511IIIll, and the heating coil preheating condition (EpXlp) is 325KVAt? , the high current density region reaches the edge meeting point (FIG. 2(a)). As a result, instability of the molten metal occurs near the collision point. In the case of 200 stores where the center-to-center distance is more than four times the pipe outer diameter, the edge-to-edge distance G is 7 mm, the preheating condition (EpXIp) by the heating coil is 352 KVA, and the difference between A wide high current density area is secured (Figure 2 ~))
. In this case, the molten metal stabilizes as the high current density region moves away from the junction. However, preheating conditions deteriorate. If the center open field ML remains 200 m and the edge distance G is reduced to 2 M, even if the preheating condition (Ep , the preheating conditions are significantly improved (FIG. 2(C)). Note that EpXIp is the plate current x plate voltage of the high frequency oscillation tube, and means the high frequency input.

Table 1 shows the welding conditions and the occurrence of welding defects when pipe manufacturing was welded using the method of the present invention, the conventional method, and the comparative method.

Nos. 1 to 7 are examples in which the method was applied to the production of 5US304 steel pipes with an outer diameter of 34 mI++ and a wall thickness of 3ffilll.

In No. 1 (conventional example), pipe manufacturing and welding is performed using ERW. Although the welding speed is maintained at 45 m/min, micro welding defects occur at a rate of 1.5/m.

Micro welding defects were recognized by the pupil in a 90° close contact flattening test.

In No. 2 to 7, after preheating the edge part with the first heating source using a high-frequency heating coil, the second heating source using a COz laser is used.
The edge abutment was melted using a heating source. Preheating was performed by checking the high frequency output so that the temperature at the meeting point was 1200°C (measured with a two-color thermometer). The CO laser had an output of 4 KW and its focus was positioned at the center of the plate thickness at a location 10 mm upstream from the center of the squeeze roll.

No, 2. 4. 5 (example of the present invention), the welding speed was 20 m/m i because the preheating conditions by the first heating source were appropriate.
At n, the inner bead height was suppressed to 0.5 mm or less, and no welding defects occurred. In addition, the preheating input is 250KVA
Limited to: On the other hand, in No. 3 (comparative example), the distance G between the edges in the first heating source was excessive, so the preheating input required 352 KVA, and the inner bead height also reached 11. In Comparative Example 6, the distance L between the centers of the heating coil and squeeze roll was too short, so the inner bead height reached inn even though the impeder was omitted. Nα7 (comparative example)
In this case, because the impeder was not omitted, the inner bead height reached 3.0 - even though other conditions were appropriate, and undercuts occurred frequently.

No. 8.9 has an outer diameter of 50.8 mff1. Wall thickness 3.5
This is an example in which the method of the present invention and the comparative method were applied to the production of M 5OS304 steel pipe. In No. 8 (method of the present invention), the height between the inner surface and the dome was suppressed to 0.5 mm, and no welding defects occurred, but in No. 9 (comparative method), the distance between the centers of the heating coil and squeeze roll was too short. Therefore, the inner bead height is 3
．． It reached between 0 and 1 undercut occurred frequently.

Nα10 to Nα12 are examples in which plasma heating is used as the second heating source. The plasma current was 160 A, and the plasma gas was Ar (m131/min). Also, in No. 12, the edge preheating part is A.
Shielded with r gas.

No, 10. 12 (Example of the present invention), the inner bead height was suppressed to 0.2M or less at a welding speed of 5m/min,
Especially for Nα12 with gas shielded preheating part, 0.08
mm, which is extremely small. Furthermore, no welding defects occurred. On the other hand, in No. 11 (comparative method), the distance G between the edges at the heating coil position is too large, so the inner bead height is 1. It reached 0mm.

〔Effect of the invention〕

The method of the present invention stabilizes the molten metal at the collision point even if the preheating temperature is increased in pipe manufacturing welding using a composite heat source, thereby preventing an increase in the height of the reinforcement and the formation of discontinuous beads. Therefore, it is possible to increase the preheating temperature, increase the welding speed, improve efficiency, and prevent a decrease in electrical efficiency, which is highly effective in reducing pipe manufacturing and welding costs.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the method of the present invention, and FIGS. 2(a) to 2(C) are plan views showing changes in the position of the high current sound intensity region as the preheating conditions change. In the figure, l: open pipe, 2: high frequency heating coil, 3
:Etsuji. Applicant: Sumitomo Metal Industries, Ltd.

Claims (1)

[Claims] 1. After preheating the opposing edges of the open pipe to a temperature below the melting point of the material by a first heating source using high frequency induction, the edge portions are heated by a second heating source near the squeeze roll. In the pipe manufacturing welding method in which the first heating source is melted and joined under pressure, an impeder is not provided in conjunction with the first heating source, and the center-to-center distance between the first heating source and the squeeze roll is at least four times the outer diameter of the pipe. A pipe manufacturing welding method using a composite heat source, characterized in that the distance between the edges at the first heat source position is 4 mm or less. 2. The pipe manufacturing and welding method using a composite heat source according to claim 1, wherein the preheating region of the edge portion by the first heat source is gas-shielded.